Unboxed Vectors of newtype'd values

Jake McArthur jake.mcarthur at gmail.com
Wed May 30 14:19:14 CEST 2012

I don't have a proposal, but I'd like to echo my support for thinking about
this problem. It is very annoying to use my own types with unboxed vectors.
On May 30, 2012 12:28 AM, "Ben Gamari" <bgamari.foss at gmail.com> wrote:

> One of the reasons I find Haskell so well suited to my work is its
> ability to easily work with large quantities of data. In particular, I
> find myself using Data.Vector.Unbox quite frequently.
> Another of my reasons for using Haskell is the type safety it
> provides. I find myself using newtypes very frequently to force myself
> to think about invariants that a more weakly typed language would allow
> me to simply ignore.
> Sadly, these two features don't interact particularly well. While the
> Data.Vector.Unbox documentation claims that "Implementing unboxed
> vectors for new data types can be very easy", it then goes on to list an
> abridged version of the Complex instance---dozens of lines of
> code. While this code certainly isn't difficult to write, it is time
> consuming, error-prone, and, above else, utterly mind deadeningly dull
> (making it quite uncharacteristic for Haskell). So dull that I generally
> avoid newtypes at all cost in code that might need to use unboxed
> vectors. This boilerplate is largely due to Vector's use of type
> families as this precludes the use of (the otherwise quite cunning)
> GeneralizedNewtypeDeriving to automatically derive the necessary
> instances.
> What can be done to fix this unfortunate state of affairs? The obvious
> solution here seems to be Template Haskell, but this seems a bit of an
> unfortunate hack around what might be a deficiency in the type families
> mechanism (or at least this application of it). The newtype package
> provides a nice mechanism to pack and unpack newtypes, but providing
> blanket Unbox instances for Newtype instances seems like an awful idea
> (and, frankly, I'm not sure how this would work with type
> families). Other than these two possibilities I am at a loss. Thoughts?
> I'd appreciate any ideas folks could offer.
> Cheers,
> - Ben
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